This invention relates to rack and pinion steering gear and to a vehicle fitted with same.
The use of power assisted rack and pinion steering gear is now well established in light vehicles such as motor cars and small commercial vans and trucks but has not yet been successfully used in heavy commercial vehicles such as large trucks or tractor units. The basic problem which has prevented the use of power assisted rack and pinion steering mechanisms in heavy commercial vehicles is the need for a small diameter pinion in order to obtain the required steering ratio, which conflicts with the need for sufficient strength and durability to withstand the heavy shock loads and power loads which are imposed on any steering gear used in a heavy commercial vehicle environment.
One proposal for overcoming the problems of using power assisted rack and pinion steering gear in heavy commercial vehicles comprised replacing the conventional track rod of the vehicle with a double ended power assisted rack and pinion steering mechanism wherein the rack had a piston rod pivotally connected to each of the opposite ends thereof and extending outwardly therefrom and wherein a tubular or solid reinforcing bar was provided which extended parallel with the rack and which was also pivotally connected at its ends to the piston rods, the said reinforcing bar serving to protect the rack and pinion from loads imposed on the steering gear and to provide a robust and substantially rigid structure extending between the wheel levers of the steerable road wheels of a vehicle. While this proposal overcame all of the problems previously encountered in trying to adapt power assisted rack and pinion steering gear for heavy commercial use, it was not commercially successful mainly due to the high cost thereof.
Another approach to the problem of providing satisfactory power assisted rack and pinion steering gear for heavy commercial vehicles has been to provide a single ended power assisted rack and pinion steering gear and to mount this between a conventional steering box and the wheel lever in place of the conventional drag link. In this arrangement the rack and pinion steering gear extends longitudinally fore-and-aft of the vehicle and has proved to be impractical both because of the length of the steering gear and because of the amount thereof which protrudes beyond the front of the vehicle or vehicles, such as large commercial trucks, wherein the driving position is at the very front of the vehicle.